Dh bought me a Kitchenaid 7QT in December.  It made very weird sounds and the whole machine started shaking while I was mixing cake batter, so back it went and they sent me another one without issue.

I used the new one for the first time to make a cake a few days ago.  It mixed the batter well - no issues.  I used it to whip up a batch of SMBC last night - that's when things got weird.  It was a triple batch but it took forever for the whites to whip up and the resulting icing was EXTREMELY unstable (like never before - separated, got runny, etc). 

I adjusted the clearance for the beater as soon as I got it, but I see that the whip is not at the correct level (i.e. doesn't even touch the dime when I did the dime test).  Does that mean that I have to use my screwdriver every time that I want to switch from the beater to the whip attachment?  Doesn't that sound weird?  I would have to clean out my bowl and re-adjust all the time.

I also find that it doesn't seem to whip very quickly (I used it last night for the first time to whip egg whites).  I put it on Level 10 and it doesn't seem to moving as quickly as my Ultra Power did which may explain why my SMBC was not right. 

Not sure what to think, but I'm bummed as the SMBC that came out of that mixer last night was TERRIBLE.  Thank goodness that I still have my Ultra Power.

My DH also bought me a 7 qt KA last May for mother's day.  I LOVE it.  I use it constantly.  I am sorry you are having problems, but wanted to add my positive review.  

AThe dime test is only done with the paddle attachment because it comes the closest to the bowl. The whisk is supposed to be a hair higher.

Ah.  I'm not sure how to gauge the speed issue though.