One problem related to engine clicking and tapping noises has been reported for the 1999 Lexus RX300. The most recently reported issues are listed below.
Had my 60,000 mile service done on my 1999 Rx300. The wife drove it when I got home and told me the car was running sluggish, didn't accelerate like it did before I brought it in. I took the car out to drive it and feel what she was telling me and noticed that when I would let off the gas and coast them give it gas there was a clunking noise. I took it to the dealer, the mechanic heard the noise and said he wasn't sure what it was. The service person said that I should just drive it normal and not try to make it clunk and it should be ok. If it kept doing it to make an appointment to bring it back. Car will be out of warranty! in 4 months.