Yeah, I like his OCD approach too, you learn so much from it.
What I was going to suggest, is why not get one of those cheap scope kits, DSO138?? It's not a real scope, it's only single channel, and compared to a real scope, its a toy. But compared to NO scope, it's surprisingly capable. It'll do audio stuff at least, and an inexpensive way to get some form of visual of what is going on. Is it accurate? No. But it is enough to give you an idea of stuff going on. I'm basically saying, if you have no scope, it's a cheap way into having something,and it isn't too big.
I got one of the kit DSO138's for about £15 I think it was, complete with a case, and actually had a lot of fun putting it together, and it gave me something to see signals.
I know the feeling of not having a scope. I just scored a cheap one last night on our favourite auction site, but as a for parts and not working. It's from a house clearance, VERY dirty, and apparently no power. I thought it would be a good project one to strip apart, clean everything, and change caps while its in bits, and test all the circuitry. I'm not expecting to have it running quickly, and be learning LOTS here testing and troubleshooting it, especially safe ways to check the high voltage parts. (I think from the service manual that there is almost 2KV (!!!) in parts of it, excluding the HT of course, which I know to be wary around.)
Anyway, I hope you find the source of your noise, and can quieten it down. Good luck and happy hunting.