I need some assistance please...

I think I may have a grounding issue and I don't know where to go from here.

I am running a 1969 yorkville tube amp through an epifani ul1x12 with a NYC epifani style speaker. (Tweeter too)

I love my 1976 p bass tone through it but every time I let go of the strings I get buzzing. If I turn the tone knob down it goes away and bye bye cool tone. I took my bass apart once already, reset the bridge and grounding wire, and a friend helped me replace the jack with helped but didn't totally get rid of the problem.

I have tried a vintage silver tone and a modern modulus and no buzzing.

Is this a single coil issue? Is it just the tone pot? If I need to replace anything what do you recommend. Thank you!