My 2003 Volvo s40 has a knocking noise on the front in. While I drive it sounds to be coming from the passenger side. I’ve been told it was my strut. I don’t know. Besides that, the car will violently shake the entire front front end but only if I take a curve To the left around 50-55mph. I can take a curve to the right 75 no problem. Well that’s my problem.

 

I guess it could be a strut, but it sounds more like control arm bushings or a bad axle to me. A visual / twisting inspection should make either of those fairly obvious. Look for the rear (large) bushing on the lower control arm to be seriously weathered and/or torn, or for there to be significant "twist" in the axle (there's some play in the transmission / differential, so look for end-to-end rotation "between parts" on the axle). If there's more than the tiniest bit of play in the axle, that's probably it.

 

Gen 1 S40s are also prone to breaking springs - look closely at the last 3 inches or so of both ends. Also should the spring break off an end, the misalignment could damage the strut mount. you should be able to see the spring by turning to full lock

 

Might have a broken strut mount - similar in design to the other FWD Volvos and make a lot of noise when the rubber breaks, Easy to test - if you can turn the nut at the top of the strut - the mount is broken. Careful compressing the spring - the S40 front springs don't compress easily with your run of the mill hand held compressor. They have a funny shape and don't compress linearly (in a straight line)

 

plus the mount needs to align correctly. Springs are very long and as hoonk noted, standard compressors don't work very well.