AER Acousticube Hissing/Noise

[adamrhowe]

Hi all, I have an old Acousticube 2 from the 90s (I think?) which sound good but suffers from hissing/noise as I turn the effects volume up - the hissing gets louder as I turn up the effects. When the effects are completely off it fortunately remains very quiet.

Does anybody know what could cause this and how I can fix it? Or is it just down to age?

Thanks