I have a 1993 5.7L Volvo. After this weekned putting the boat up when I went to turn key on to lower the drive I noticed the tach go all the way over, when I pulled the engine cover I heard a humming noise coming from the distributor. I merely pushed on the cap and it would stop and the tach would go back to zero, once I stopped pushing against the housing it would start again. Any suggestions or answers would be appreciated.