Q I wanted to copy some old cassette tapes to my Mac, so bought a USB transfer system to make this easy. However when in use, it makes a continuous rapid throbbing sound, a bit like a slow motorbike, which becomes still more obtrusive during quiet passages in music and between tracks. This sound is generated even when the tape drive is not running, and whether the system is connected by USB or analogue audio input. However switching from the Bose external speakers to my Mac’s internal speaker abolishes the sound altogether. What is causing it, and how can I get rid of this noise?

A This is almost certainly an electrical interference problem, most probably arising from poor electrical shielding or grounding of the motor in the tape deck. The cable to your Bose loudspeakers is then picking this electrical noise up.

Although these tape and record deck recording systems look quite natty, internally most are not particularly well engineered compared to even amateur quality audio components.

An electronics professional may be able to locate the source of the interference and ensure that it is properly shielded and/or grounded, but the simplest solution is to use high-quality well-shielded speaker cables, which should not pick up this or other forms of interference.

Updated from the original, which was first published in MacUser volume 26 issue 11, 2010.