Curious Noise Problem with HP P2015DN Laser Printer

[JonSea]

This printer has been sitting unused in the corner a couple years but I'm getting things organized and want to put it back to work. But it's got a weird, annoying noise problem.

This is one of the printers that essentially stops everything, or at least everything mechanical, between print jobs and in the past was virtually silent. Now, it works great and prints perfectly (it's only printed about 7000 pages total), but when it's idle, it makes kind of a loud white noise sound. As best I can tell, nothing mechanical is in motion when it's making this noise. Pulling the toner cartridge and paper tray doesn't change anything

Now, the weird part. When the ethernet cable is disconnected, the character of the noise changes. With ethernet disconnected, the sound changes to more of a buzz, with a medium frequency tone (not line frequency, more like 1000Hz). When ethernet is connected, the noise follows the negotiating process, locking into the white noise sound when synced to 100Mbps.

This noise doesn't appear to come from the board where the ethernet connection is made, but more from the center of the printer...which protects its secret well. It will be a major project to get to the inside part of the printer.

One thought is that it's a power supply issue, somehow responding to load, but this seems a little unlikely as the noise follows in perfect sync with the ethernet speed negotiation process. Anybody seen anything like this before? Any ideas?

The printer is close to the network gear, a networked amp and a couple Raspberry Pi boards acting as a music player and NAS.

 

[gophert]

if it is not plugged in, it is in standby mode. Depending on the exact sound, it could be the fuser - they sometimes buzz when they are about to bite the dust - or something caught in the fan. You can use a piece of tissue paper to see if your u it has a fan in that area (does it suck/blow the paper at the vent holes).

 

[JonSea]

There is a fan on the side. It shuts down when the printer is not printing. It may be a fuser problem.

Some research reveals many HP lasers have an issue with power supply noise - HP doesn't admit there's an issue but often will replace printers if they get enough complaints. I couldn't find anything about a fix for this problem. One guy put in a spacer to push against the power supply box to cure/reduce the problem but nobody could reproduce that fix.

My "fix" for the moment is a wifi-controlled switch so that Google can turn it off when not in use.

 

[Mickster]

Maybe try dribbling some hot-snot over the windings of any toroidal-inductors you can see in the PSU?
If it ain't that, it's one more thing you can rule out.
EDIT:
Some RC model ESC's deliberately use the windings of a BLDC motor to provide acoustic feedback when initializing, or changing parameters within in a setup routine. Could the ethernet hand-shaking be causing a similar, unintended, effect on the PSU?

 

[JonSea]

It's possible, but it never did it before. It was virtually silent when idle.

It's got one of these "instant start" fusers - it takes only 10s of seconds from power up to printing.