[Brian 162]

Hi all
I've got a front end noise/vibration that i'm having trouble diagnosing.
I'll try and keep it brief.
I was going to DIY the front brakes on my Tahoe. I tried removing the guide pin on the lf caliper. It wouldn't budge (Canadian winters). I tried heat still no go. I gave up put the tire back on. From that moment now I have a vibration around 45 mph and higher. When the brake is applied the noise increases.
I took the vehicle to my mechanic, he replaced pads, rotors. The noise is still there.
I took it back and he said the front diff is the culprit and installed used one from salvage yard. The noise is still there.
I still think it's something with the caliper but he says it can't be.
I've used this shop for 20 years and this is the first time I've had an issue with them.
Any ideas from the GM brain trust?

Thanks in advance
Brian