I have a '99 Tacoma that has developed a loud clicking or snapping if the blower motor is turned on. I could first hear it when driving at an RPM of at least 2K. It clicks like this every minute or 2 while driving as long as the blower motor is on. Under a load such as going up a steep hill it seems like it even causes a hard engine miss. I just discovered the other day that I can duplicate the noise when parked by running the engine at 2000-2500 RPM and turning the blower on. You really can't hear anything at normal idle speed. I had my wife keep turning it on and off at 2-2500 RPM while I tried to find out where the clicking is coming from but I couldn't find it under the hood. I'm wondering if it's coming from under the firewall/dash area.

Does anybody know what I'm hearing and why it would click like that periodically while driving or why it would affect performance?