Met with Karl and was shown where the crawl space was. Discussed the issue and sound they where experiencing. Cycled the solenoid valve 15 times and the only noise I herd other that the furnace running was the drain/condensate pump running. Verified with Karl and his wife and the noise would not present while I was here. Gave customer an estimate for replacement of the solenoid valve. Customer opted to just pay the trip fee at this time.