That 2600 has seen some abuse over the years, no doubt. Ever break one of the sliders? (guess what I did...)
I'm pretty gentle with the synth overall. One of my sliders is a bit noisy but it's not one I use a lot (left reverb slider). The way it makes noise is somewhat strange though I think it might not be the slider. You can get replacement sliders for the 2600 and they aren't too hard to replace. You can probably get a local tech to do it for not too much money or just try it yourself.
Have me morning coffee! Just plugged in! Going to give it a go! Thanks! Cheers!;-)!
This patch didn't really go as planned but there is much that can be done here. Thanks for commenting!