My 1999 Lexus 400 engine has a knock, sounds like it's coming from the drivers side of the engine. IUt's not inside the engine. I had the oil changed, I was using Castro 20-50W oil and the service center replaced it with Penn's oil 10-30W. Ever since the oil change the knock has started. Whenever I turn my wheels it's much louder. It's also louder when the engine is cold.I don't know if it's my power steerin g pulley or not. I thought my power steering unit was on the psg. side beneath the P.S. reservoir.

Check you motor and transmission mounts. If one or more is broken they will make noise. You can tell easily by reving the engine up in park and see if the engine lifts up more than a inch
Also the rack & pinion mounts can be loose if the engine mounts are fine

Sounds like you have the wrong oil type. The 10W30 is a thicker oil and takes a little longer to heat up and lubricate as it should. The 20W50 sounds like it would be thicker but actually isn't. Replace the oil with the proper oil type and it should resolve the issue. Although the steering information kind of throws off the diagnoses since that points to the power steering pump and rack and pinion steering cylinder. To make sure check the fluid level in the power steering pump and make sure they didn't goof and put motor oil in that. If they did go back to them and make them replace all the components they just destroyed. Your vehicle was designed to use 20W50 and you should always use that unless temperature makes it a better choice for the thicker 10W30. If you lived in a desert climate where it stayed hot year round 10W30 would make sense but for normal operations you should always use the recommended oil in the engine. Thicker oils cause the oil pump to work too hard and cause damage to the motor when parts are not lubricated correctly.