One problem related to engine clicking and tapping noises has been reported for the 1999 Volvo S70. The most recently reported issues are listed below.
Vehicle has electrical/brake and engine problems. Brake pedal has a clicking noise, and after the third click, brake pedal locks up. Also, engine failed twice. Failure a result of the engine flooding itself, ruining the spark plugs. Dealer does not know what the problem is. Engine was replaced. Brakes will also occasionally sink into the floor. These problems still exist after being repaired twice. In addition the electrical system has failed several times--the turn signals went out, both headlights have gone out, and the gear shift panel lights have gone out.