Any unusual noises coming from your electric shower warrant attention. It could indicate loose components, limescale buildup, or a more serious internal issue. Consult an electrician for inspection.
With the assumption being every electric shower we've seen (besides Aqualiser) have been in zone 1 of the bathroom, you would want a qualified electrician undertaking the work, 1) To ensure the safety of the shower where you're bringing mains voltage in close proximity to water and 2) so they can sign off their work and notify building control.
