Got my portastudio a while back, used the shit out of it, a few months later noticed Track 1 starting to have a hard time recording. The input into the line was fine, levels were metering correctly, but when I went to play back the recording, it started to appear grainy and wavy and quiet. The more I recorded on it, the quieter and worse it got. I put it away for a few months. When I returned and tried it just for fun, track 1 was working just like new. I ran it for a while. Now, I picked it up after a few more months of inaction, and track 1 is back to its old issue. Line is good, metering is good, just having issues recording audio properly. Sound is diluted and wavy and unstable. Any and all advice would be helpful.