Whyy does Hiwatt solidstate pick up radio?

[frank57]

I have this Bulldog 30r amp which keeps picking up the radio from time to time.
Some repair guy slashed the tracks where the input jacks are and connected the grounds from low to high input.
Not sure why.It doesn't really solve the issue 100%.It keeps coming back.
But how exactly are the jacks grounded? To the chassis?Are there grid stoppers?
I've drawn out the board.
I was thinking to take the jack off the board and run a a shielded wire to a bolt somewhere on the chassis,
unless this might create a ground loop.