This is at least the fifth topic generated about a similar noise since the weather has gotten really cold. SInce we can't hear the noise, it culd be several things, but the simplest things are the first to look for. Check for rub marks inside the strut tower, up at the very top where the spring pad comes close to and may possibly rub against the outboard side of the strut tower. When it gets cold, the rubber gets harder and tends to make a lot of noise. If this is the case, all you need to do is put some silicone grease (Sil-Glyde) in the interference area to lubricate the rubber and steel interface.
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Scott
1991, 254K miles, glass hood, police grill, SVO shifter, Catz fogs,
K&N, 73mm MAF, Superchip, PP Y-pipe, Borla cat-back, 190 lph pump
Eibach/Tokico/polyurethane, SHO Shop front & rear strut braces,
16x7.5" Moda R1, 225/55ZR16 Bridgestone RE730, -1 deg camber x 4,
6 disc CD, Class II hitch, Silver award at SHOklahoma Car Show