Clanking noise heard when braking at low speed and taking off

Likely picked up a foreign object in the pad. Pull the pads and make sure no rocks are there. You can ignore the groove.

Spin that wheel by hand as fast as you can. If you can hear the noise coming from right behind the tire it's probably a wheel bearing.

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Visit the on-line store, known as reliable-store, they have the repair manuals. I'm sure you will get the solution of your problem. 1999 lexus rx300

mate sounds like u needa find ya self a good mechanic and stick to them only, have u checked your oil mite need a top up or a change

if you are traveling at more then 2000 rpms when it starting to cut out change the fuel filter it's clogged
if you are haveing the problem at low speed have the fuel pump checked,,, if everything is fine you have a ignition problem

Any grinding is not good. This almost sounds like a sticking brake rotor/caliper which is popping free, or a parking brake dragging. Either way the fact that it stops does not mean it will fix it self. I would inspect all 4 brake rotors for excess wear.
try to determine if this happens after parking and braking, then isolate the area you thing the noise is coming from.
Separate from that it could be a gear issue in your trans at low speed but you need to get it checked ASAP as it will only lead to greater expense.

that means they are 6/32 so i would let them go lower you still got alot of life let in them,,,i would go to 2/32,,you should hear the brakes squealing when they are really low,,you should get another 6000 out of the ones on your car now,i ouwld wait alittle,just have them checked every oil change

Your tranny need to be repaired at once. The tranny is slipping. Some Lexus owners do have the similar problem including myself.

Every 90,000 miles or 72 months per manufacturers recommendations.

Please clarify!