This is a long shot to describe, but here goes. I just got my guitar back, a Fender Big Block Stratocaster, from getting it setup at a guitar shop: Long & McQuade. I plug it into ANY of my amps and when I put the volume knob on my guitar to 10 as I always have, I'm welcomed by this incredibly loud screeching sound. This also occurs when I switch pickups. It is least noticeable on the humbucker (Fender Enforcer), but still screeches. It screeches louder and won't stop at all when I switch it to any of the other pickup positions. The only way I stop it is by turning down the volume knob to 0. I only got this sound with this guitar after getting it setup; before it was setup it didn't do this. They claimed they did not do anything under the pickguard as it was just a typical setup.

The odd thing was that the first time I tried this Strat at the store, there wasn't this issue and I never had it prior to having it setup. The really weird thing is that when the guy plugged in another Big Block they had in stock when I brought it back to them, it had this same issue; the annoying screeching noises. This is just so confusing.

So here are the facts: It never occurred before with the one I tried out and the one I have, but now it's occurred in the one they had in stock as well as the one I have now. The tech said that it is due to the fact that the Big Block has a metal pickguard, but I do not really believe this as many guitars have metal pickguards and I doubt have this issue. But I can't really think of what could the other reasons be. It's just so weird that it didn't have the issue before, and all of a sudden they have it! It really just shut me up when he plugged in the same guitar and it had the same issue, when I tried it only three months earlier and there was nothing wrong with it. I'm completely perplexed. Please help me out. I just bought this guitar brand new a mere three months ago. They also told me that they did not fool around with any of the electronics neither, as I said they also took out another Big Block and proved to me the problem. Odd.

Please help me out! Any help will be grateful.

If necessary, I can send a brief video outlining the issue if you want to go in detail to help me. Just e-mail. Thank you.