Quite a while back I worked for an electronics maintenance company and we’d regularly get computer terminals from a company in Avonmouth (where the cars are) which were “making hissing and cracking noises”.
The cause was the EHT (12,000 volts or so) sparking across the insulation in the moist air.
A liberal coating of spray plastic sealant fixed it, but the air is definitely damp down there.