I had a customer coming over to pick up a radio that I had advertised for sale. Since I hadn't played it in a while I plugged it in and turned it on. It sounded awful. Not at all like I remembered. Slight panic setting in, I took the back off to see if it was anything obvious. Added an antenna wire to see if it improved. No. Fiddled with it for a while than tried playing a set that I was working on that I knew was good. It too sound bad. Something was interfering with the signal. I had added a small 200W heater that wasn't on. I unplugged it, no difference. My customer would be here shortly. I had an old desktop computer that I set up just for radio info. It was not turned on. Unplugged it, interference was gone. Plugged it back in interference. I've had another computer in my work area before that had recently past away, and it didn't do any of that, on or off. A little puzzled but had a happy customer.

My biggest noise problem was outdoor dawn to dusk motion sensing lights.
We had to replace them after construction, I bought two lights and tested them
for noise output. One had just a little noise output, the other was very quiet,
so I went and bought four more for installation.
Mikek

Most computers for about the last 20 years have a 5V standby power supply. That is how they can get by with a simple push button power switch instead of something that switches the 120VAC power. Your standby supply may have been noisy when new but they often have failing capacitors after they have been running continuously for several years. Here in Austin, I would go to the Goodwill computer store and get a different power supply to try. If you don't have a Goodwill, you may be able to find something on eBay.

Jay

It might have gone some way to forestall a potential service call to demonstrate his radio with and without that interference so he could be aware of how problems like that crop up, and what to do about them. As you demonstrated to yourself, we all need to be reminded that we have so many more sources of interference these days than were present when these old radios were built...you started to take it apart when the problem was external to the radio!