I also have a 91 Supra 7mgte mine would off and on make a noice in the top end ..the lifters did a oil change and it made it worse from what you have described and from my experiance it was my oil pump.also I have a 86.5 mk3 7mge that is my prodgect car right now I want to turbo it . ... hope this helps you or the next person that has problems