EDIT/SOLVED: The culprit turned out to be a faulty offbrand 5V 3A DC power adapter. I tried another adapter - incidentally, one that I use to charge my smartphone - and the hissing sound was gone. My other router - also a Raspberry Pi 4B - uses the same power adapter as the one that started malfunctioning/hissing was using, but it is quiet and operates normally. At the very least I draw the following three conclusions:

1. 5V 3A is enough to run a Raspberry Pi 4B as a router with constant heavy TX/RX of at least a couple of terabytes per day.
2. I should be prepared for the other offbrand power adapter - namely the one that came with the OkDo bundle - to fail within a year or so.
3. There are really nice people here that give quick and elaborate responses! Thank you all! 🩵

The linked file is a recording of a hissing sound that my Raspberry Pi 4 started to make sometime during the last 24 hours. Another symptom is that the power on and CPU activity LEDs are out. It is not running hot. It doesn’t have an internal fan. It is being cooled by six PC chassis fans. It is running OpenWRT. It has been pumping Linux ISOs in and out non stop for about four months.

I have tried cleaning it by dedusting it. I have also tried rebooting it. While rebooting, it squeals like a mouse, like it was suffering but the LEDs function properly. As soon as it loads user space though and resume routing, they turn off and the hissing sound continues.

Here are some system logs with severities warning and error. As you can see, the logs are from the 15th and I don’t think any of them pertain to the hissing sound and/or the LEDs.

WARNING  
[May 15, 2026, 23:29:12 GMT+2] kern.warn: [    0.196065] pci_bus 0000:01: supply vpcie3v3 not found, using dummy regulator  
[May 15, 2026, 23:29:12 GMT+2] kern.warn: [    0.196201] pci_bus 0000:01: supply vpcie3v3aux not found, using dummy regulator  
[May 15, 2026, 23:29:12 GMT+2] kern.warn: [    0.196257] pci_bus 0000:01: supply vpcie12v not found, using dummy regulator  
[May 15, 2026, 23:29:12 GMT+2] user.warn: [    7.225917] urandom-seed: Seeding with /etc/urandom.seed  
[May 15, 2026, 23:29:12 GMT+2] kern.warn: [    8.327998] snd_bcm2835: module is from the staging directory, the quality is unknown, you have been warned.  
[May 15, 2026, 23:29:12 GMT+2] kern.warn: [    8.365104] brcmutil: loading out-of-tree module taints kernel.  
[May 15, 2026, 23:29:12 GMT+2] kern.warn: [    8.780919] brcmfmac mmc1:0001:1: Direct firmware load for brcm/brcmfmac43455-sdio.raspberrypi,4-model-b.bin failed with error -2  
[May 15, 2026, 23:29:12 GMT+2] kern.warn: [    8.792642] brcmfmac mmc1:0001:1: Falling back to sysfs fallback for: brcm/brcmfmac43455-sdio.raspberrypi,4-model-b.bin  
[May 15, 2026, 23:29:12 GMT+2] daemon.warn: dnsmasq[1]: no servers found in /tmp/resolv.conf.d/resolv.conf.auto, will retry  
[May 15, 2026, 23:29:18 GMT+2] daemon.warn: dnsmasq[1]: no servers found in /tmp/resolv.conf.d/resolv.conf.auto, will retry  
[May 15, 2026, 23:29:21 GMT+2] daemon.warn: odhcpd[990]: No default route present, setting ra_lifetime to 0!  
[May 15, 2026, 23:29:21 GMT+2] daemon.warn: odhcpd[990]: rfc9096: br-lan: piofile updated  
[May 15, 2026, 23:29:37 GMT+2] daemon.warn: odhcpd[990]: No default route present, setting ra_lifetime to 0!  
[May 15, 2026, 23:29:53 GMT+2] daemon.warn: odhcpd[990]: No default route present, setting ra_lifetime to 0!  
[May 15, 2026, 23:30:18 GMT+2] daemon.warn: odhcpd[990]: No default route present, setting ra_lifetime to 0!  

ERROR  
[May 15, 2026, 23:29:12 GMT+2] kern.err: [    0.307942] bcm2708_fb soc:fb: Unable to determine number of FBs. Disabling driver.  
[May 15, 2026, 23:29:12 GMT+2] kern.err: [    0.307968] bcm2708_fb soc:fb: probe with driver bcm2708_fb failed with error -2  
[May 15, 2026, 23:29:12 GMT+2] user.err: [    7.197094] insmod: module is already loaded - fat  
[May 15, 2026, 23:29:12 GMT+2] user.err: [    7.204851] insmod: module is already loaded - vfat  
[May 15, 2026, 23:29:22 GMT+2] daemon.err: procd: Got unexpected signal 1  

Judging by the squealing during reboot, I believe it to be either the CPU or memory, although I have never hears memory make sound, while CPUs, I have.

Edit: The solution in my case was to run these commands:

sudo apt update
sudo apt install linux-image-rpi-v8 linux-headers-rpi-v8

The new kernel wasn't used after rebooting though, so I had to edit /boot/config.txt and add:

# New kernel (test)
kernel=vmlinuz-6.12.75+rpt-rpi-v8
initramfs initrd.img-6.12.75+rpt-rpi-v8 followkernel

I'll figure out how to make it so I don't have to manually keep config.txt updated but for now, I'm happy to have a process to stay up to date with current kernels.

/edit

Reading about the latest Copy Fail security vulnerability I realised I was overdue a check on my system. It turns out I had even bigger problems - I was still on Debian 10/Buster.

To solve it I updated my apt list to contain: deb http://archive.raspberrypi.org/debian/ bookworm main

But after doing this, updating and doing a full upgrade, my kernel is still 6.1.21.

I'm now reading that I should not have upgraded from bullseye to bookworm, so what is the easiest way forward from here? If there is a documented set of steps for this scenario I'd appreciate a link. I have a lot of services and scripts so reinstalling from scratch is not really an option.

uname -a
Linux 6.1.21-v8+ #1642 SMP PREEMPT Mon Apr 3 17:24:16 BST 2023 aarch64 GNU/Linux.

cat /etc/os-release
PRETTY_NAME="Debian GNU/Linux 12 (bookworm)"``___

The United States FCC recently announced a ban on new consumer-grade routers produced outside of the US. This does not affect existing devices that were already authorized, and there is a carve-out for manufacturers to apply for a conditional approval. It's difficult to say what the medium or longterm effects of the ban will be.

This got me thinking about what could be used as a makeshift router in a pinch. As it so happens, any computer that can run Linux and has networking interfaces can function as a router. This blog post by Noah Baily documents the process using various old computers and components as custom routers over the years.

These makeshift routers are not going to win any bandwidth speed races, but they're perfectly capable of routing traffic for IoT devices or basic browsing. They're also useful for capturing traffic to analyze or sharing internet access from WiFi to Ethernet or vice-versa.

This guide documents the setup process and capabilities of using a Raspberry Pi as a router. It does not require a particularly powerful computer, even the older Pi 3 B+ that lots of us have tucked away in an old parts bin works fine for this.

This board turns a Raspberry Pi CM5 into a NAS with support for 5 HDDs

Hi all, I'm trying to figure out a good easy setup for a baby monitor, I've got a pi4, pi camera 2 noir, but it's too dark to see anything by itself, and it feels like I'm leaving the plug & play zone where I could just google & program, and am entering the buy an LED and solder zone, which scares me. Any suggestions?

Although [Thomas] really likes the Raspberry Pi Pico 2 and the RP2350 MCU, he absolutely, totally, really doesn’t like the micro-USB connector on it. Hence he jumped on the opportunity to source a Pico 2 clone board with the same MCU but with a USB-C connector from AliExpress. After receiving the new board, he set about comparing the two to see whether the clone board was worth it after all. In the accompanying video you can get even more details on why you should avoid this particular clone board.

In the video the respective components of both boards are analyzed and compared to see how they stack up. The worst issues with the clone Pico 2 board are an improper USB trace impedance at 130 Ω with also a cut ground plane below it that won’t do signal integrity any favors.

There is also an issue with the buck converter routing for the RP2350 with an unconnected pin (VREG_FB) despite the recommended layout in the RP2350 datasheet. Power supply issues continue with the used LN3440 DC-DC converter which can source 800 mA instead of the 1A of the Pico 2 version and performed rather poorly during load tests, with one board dying at 800 mA load.

Two months ago, we announced increases to the prices of some Raspberry Pi 4 and 5 products. These were driven by an unprecedented rise in the cost of LPDDR4 memory, thanks to competition for memory fab capacity from the AI infrastructure roll-out.

Price rises have accelerated as we enter 2026, and the cost of some parts has more than doubled over the last quarter. As a result, we now need to make further increases to our own pricing, affecting all Raspberry Pi 4 and 5, and Compute Module 4 and 5, products that have 2GB or more of memory.

The Raspberry Pi has been a revolutionary computer in the maker space, providing a full Linux environment, GUI, and tons of GPIO and other interfacing protocols at a considerably low price. This wasn’t its original intended goal, though. Back in the early 2010s it was supposed to be an educational tool for students first, not necessarily a go-to for every electronics project imaginable. As such there are a few issues with the platform when being used this way, and [Vin] addresses his problems with its power management in his latest project.

mkdir -p ~/.local/share/file-manager/actions

nano ~/.local/share/file-manager/actions/qrcp.desktop

[Desktop Entry]
Type=Action
Name=Send with qrcp
Icon=utilities-terminal
Profiles=profile-one;

[X-Action-Profile profile-one]
MimeTypes=all/all;
Exec=lxterminal -e qrcp %F