Is this a another strut?

That is your quad shocks which helps prevent wheel hop. I wouldn't think a squeak would be coming from those. I would look more at your ball joints if it is coming from the suspension.

Well, the squeak could be lots of things, heck we need a another forum just for squeaks w/these cars.
1. Check for slight leaks out of your axle housings. Rear oil from the "pumpkin" or Differential housing could cause glazing of the break pads and rotors. If there is a leak, there should be dark water like pattern on your dust shield. The only fix would be new rotors and pads and axle bearings and seals.
2. Front sway bar, just grease, I find White lithium grease to be to thin, anything thicker and water resistant should do.
3. Just find anything rubber and grease underneath the car. Now a squeak can be confused w/a metal to metal squeal, b/c some break pads have little metal pieces in them. So, make sure its not your exhaust rubbing on the soft underbody.
4. Plus one on the ball joints, you can do your side to side test w/the car in the air, any play in the will new ball joints must be considered. From my experience ball joints start to tick when your turn, and slight thump at stopping the vehicle.
5. Outer Tie rods, they can squeak as well, regrease with a grease gun w/needle or change w/alighnment.
6. Front control arms bushings, replace bushings and or grease.
My vote would be your brakes and rotors, if the squeak is in the rear. I had the fore mentioned #1. The brake pads were changed, but not the rotors, so every time I hit a slight bump; SQUEAK!

bigboytraks:

+1 for what the demon said.

Here's another one for the list:

The e-brake cables pass through the floorpan and the cable is protected by a rubber sleeve. These things will squeak as you go over a tiny bump. A little silicone lube on the sleeve (once a year or two) is all that you need to bring peace and quiet from the e-brake cables.

Leave those quad-shocks on unless you get aftermarket lower control arms. But the aftermarket LCA's can transmit more noise into the cabin. Decisions, decisions, ....

HTH,

Chris

You need a new mechanic...if he doesn't know what those are.
Squeaks are often caused by bushings that are worn, dried out, out of shape, etc. It's really hard to isolate the sound unless you have a friend that is willing to ride underneath your car as you try to recreate the noise. So do the next best thing. See if you can determine is it in the front or the rear? Left or Right side? Try walking over speed bumps to help determine. Does the problem go away if you spray the bushing(s) with WD-40 or white lithium grease? If so, you've found the offender...replace it or, if it has a zerk fitting, grease 'er up.
ALSO, I hope your mechanic didn't charge you for 4 new struts. You only have 2, in the front. The rear has a pair of good old fashion shocks. Shocks are CHEAPER than struts. It worries me the way some mechanics prey on individuals who don't know everything about their car. Can I ask how much did you pay for the set including installation? And were they OEM replacements, aftermarket, or ???
Best of Luck and WELCOME to StangNet!