I have the same problem on my 97. At speeds less than 45mph the left front end has a moderately heavy rattle, but above this speed it seems to disappear.
How about this possibility: Loose wheel bearing!
I have a 93 Dodge van to pull a popup camper and I had the same problem. I was lucky when a mechanic decided my wheel bearings needed to be adjusted. This completely stopped the rattle in the front end. Before this, I had multiple possibilities, but not one of them included a loose bearing. Apparently, this should be adjusted during a brake job. If the brakes were replaced, but the bearings not greased and reseated correctly this may be an inexpensive fix (~$35).
I'm going to have the front end looked at, but have the bearings looked at too.
This has really been a great discussion, I am on wednesday going to have a local shop here look at the front end and see if there is play in the ball joints, if it is the problem I'm going to replace them and see what happens, as far as the berrings, I never thought of that. It will definantly be something I will check, at the same time i do the ball joints I'm going to be replacing the front and rear rotors and brake pads while repacking the berrings. I'll keep you all posted, hope this all fixes it
Ok had the car in the shop today, they checked all of the lower suspension and said everything is tight like it should be, I really trust this guy who looked at it, he never has steered me wrong before and I've been taking my car to him for years. So here is the deal he says he is 90 percent sure it is the strut mounts. So I just bought new struts from NAPA for Sensa Track @ $63.00 a peice its not too bad concidering the car has 108,000 miles on it I can't really go wrong, so I'm gonna repace those on the front this weekend, and repact the front berrings, if the knocking in the front end on small bumps does not go away then I'll keep searching for the problem, but I'm pretty sure this is the problem as well. Keeping ya'll posted
If you open the hood, you can see the bolt that holds the strut in place, try holding on to that plate and twist it. I just noticed that mine seems to be loose. I don't know if it's suppose to be like that, i didn't try to tighten the nut because i don't have a wrench that size, but tomorrow, i'll try to tighten it and see if it will move. I don't know if the design is like that but you can actually twist the plate but won't really turn because the strut is attached the the control arm, but if its moving like that how much more a bump will do to it. I guess we can inquire about this if it's the design of the car or is it something we have to fix.
The bolt in the middle of the strut on top just holds the top plate to the spring and will turn... My 1998 catera has the same problem, small potholes or my driveway at low speed like 10mph causes a voilent CHUNK sound! If somebody figures it out pls post it!
Just to update on the problem, I just had all the bushings replaced on the front lower control arm and then replaced both the sway bar link as well and everything is solved. Had the car aligned and I could not be happier. Just as posted in the Yahoo site about the bushings, I had both my rear bushings split. Alignment though gave me a very big headache because all of the tie rods in both the front and the rear are stuck. The mechanic doing the alignment suggested that i buy a new set which would cost me a lot. They wouldn't touch the tie rods or even try to force them to move because of fear that the joints might give. I decided to remove all of the tie rods myself one by one and used two pipe wrench and some extension to the handle of the pipe wrench to give me some more leverage and I was able to move the stuck tie rods. It was like doing a very hard work out. At least i saved a lot of money and the alignment was finally done and i think i grew some muscles at the same time.
I had the same noise on my Catera and i just changed the sway bar end links and the upper bearing plate of the strut and the noise is gone. The Sway bar end link is about 105.00. I would do this first.
AS FOR OVERHEATING ISSUES YOU MUST GET RID OF THE THE DEXCOOL COOLANT. Go under google and read all the problems with Dexcool.
Its not a dexcool problem just because it is posted on google. If dexcool was junk GM would have stopped using it years ago. The Catera has a bulletin out to reprogram the instrument cluster because the GAUGE is reading wrong---looking like overheat when it really is fine.
My front end noise turned out to be a "link pin." The part is located in the frame of the strut assembly. It runs parallel to the strut. When you test the struts by pushing down on the car you may mistake the noise for the strut. Inexpensive fix (<$150)
Re: strut mounts??? 
