i had a problem kinda like that, sometimes when i turned the volume up it would actually get quieter and vice versa. probably just the head unit breaking. the clock also quit working on mine. i had one that i put in and it's all good now. maybe it's the speed compensation messing up. my advice would be to replace it, you'll defintely save yourself a headache and if you shop around it won't be all that expensive. good head units are like $100 - $140, generic replacements can be as cheap as $20. it'll sound a whole lot better too
