Hi Nellie, Yes the problem is usually dust or grime build up in one area and it gets very scratchy...The pot has a little carbon arm that runs around a copper slip ring altering the resistance (A variable resister)
To clean do as follows. Access the pot side of the pot and where the lugs are get some rubbing alcohol (Isopropyl alcohol)dip a cotton bud in the alcohol and press at the orifice by the lugs move the control back and forth several times until the noise disappears. I have made a very rough drawing.and I mean rough..Thankfully I am a better musician than a artist ha ha
fenderphil