does it go up and down and make the noise or not go anywhere at all. if it still mvoes try lubing it. if it doesnt - - order a new one.

I recently reversed out the 850 and the garage door was still down far enough to catch the antenna; it bent the tubes and then started grinding when the motor was activated. I gently bent them back and lubed them up and it was OK; I had to force the movement up & down a couple of times to get the antenna to expand/retract properly, but in the end it worked.

Check to see if your antenna is bent by having the radio on then rotating the antenna in it's socket by hand and seeing if it moves out of axis when you rotate it. If it does, then this may be your problem and it will cause the mechanism to grind. You can bend it back, but beware as this metal is thin and delicate! Heaps of WD40/penetrating oil is useful here.

Beats replacing the antenna unit...
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Michael in Sydney -> http://au.geocities.com/ozbrick850

try wd-40 on the mast. what i did was first spray the wd on a rag and wipe the whole antenae, then turn off the radio and run over and spray the wd at the bottom as the anntenae goes down. should work fine. may have to repeat once in a while (after car wash, etc.)