You need to trigger the sound only once within your loop, and only if it's not playing already. use something like
if sound playing(n)=0 then play sound [n]
Or maybe you're better off using loop sound if it's to be constant.
Also it might be simpler (and sound cooler) to use a 3d sound for something like that, and position it at the same location as your sprite object (not sure how you're doing your sprite though)
Also If you'd posted your problem code I wouldn't be wasting my time guessing all this, it'd be fixed right now
ZX Spectrum 48k Issue 3, Radio shack Tape drive, Rank arena 12" T.V. set.