Had transmission rebuilt about two weeks ago in my 2000 Lexus RX300 SUV. Had valve cover gaskets replaced. Had an oil change. 5W30 was used instead of 10W30. My low oil pressure warning light came on and car was knocking under the hood. Had enough oil. Oil changed to 10W30. Next day car was humming loud and warning light came on. Car started running normally in about ten minutes and warning light went out Now when I start the car in the AM, it makes a ringing (shrill) noise, no warning light. What is the problem with my car? Thanks.