I'd guess it is the relay for the turn signal going bad. Or a speaker
wire has somehow crossed into the turn signal system. I'd have to hear
where the buzzing is coming from.
Try changing the turn signal relay first. It is cheap, and probably
easy enough for her to do since it just plugs in somewhere. The trick
is finding where.
Good luck!
Bill
>> Stay informed about: Turn Signals Buzzzz ('93 300E)