so ive been chasing this problem for about three weeks now and im starting to lose my mind a little. my 7300 started showing elevated noise floor on 40m and 80m, like S2-S3 consistently even with the antenna disconnected. at first i thought it was RFI from something in the house so i went around unplugging stuff one by one, the usual routine. didnt change anything.

then i noticed it's worse when the shack computer is on but even with the computer completely off and unplugged it's still sitting there. the bands above 40m seem mostly fine, 20m maybe has a tiny bit more noise than usual but nothing dramatic. just 40 and 80 that are bad. i've done a factory reset twice, updated the firmware, tried a different antenna feedline, even borrowed a buddies dummy load to rule out the antenna entirely. noise is still there with the dummy load connected.

at this point im wondering if something inside the radio itself has gone south. maybe a filter cap somewhere or something in the front end? the radio is about 4 years old and has been running pretty much every day. any ideas before i ship it off to icom?

Before you ship it anywhere I'd pull the top cover and just look around. Four years of daily use can cook a few things. On the 7300 the frontend is pretty robust but I've seen the TCXO area get a little flaky and cause weird noise behavior, though usually that manifests differently than what you're describing.

The 40/80 thing being specific to those bands and not the higher ones is actually a useful clue. Those bands share some frontend filtering paths that differ from the higher bands. If you have a scope or even a cheap SDR you could use as a secondary receiver, try listening to the IF output on the 7300 while you poke around — sometimes you can localize it that way. Also worth checking the band pass filter board connections, the ribbon cables on that radio can develop intermittent contact after a few years of thermal cycling. Just reseat everything gently. Might be nothing but its a 10 minute job before you box it up.

had something similar on mine last year, turned out to be a switching power supply in a USB hub literally two feet from the radio. even with everything else off that hub was still powered because it was on a different circuit. just mentioning it because you said computer off but didnt say everything on that desk. those cheap USB hubs are brutal on 40m.