[MR2] radio question, mk2t

[Chris S]

Ok, this is a strange one.  I have stock toyota 5mm wires (3rd gen engine using 93+plugwires), NGK bkr6e plugs (stock heat range, copper, resistor).  I have used this setup for the last year and a similar stock setup with th eoriginal 3sgte.

I say this bc i have discovered an odd problem.  My radio has developed a 'ticking' sound that is RPM dependent.  I don't know what's changed on my car to suddenly cause this, but it is very annoying.  The engine is a relatively stock 3rd gen, the radio is a stock 91 premium system (7 speaker cd/tape), and the issue just developed recently.  the car runs smoothly, no issues with gas mileage/driving, etc, but there is just this noisy ticking sound in the radio.  It is most noticeable on the weaker stations, still noticeable on the strong ones, and not noticeable at all when playing a cd.  

any tips?
chris