Parts of London Underground (LU) are so noisy they could damage people's hearing, a BBC investigation found.
Professor Deepak Prasher took readings on the Victoria Line
An expert measured sound levels louder than a pneumatic drill and advised regular passengers to consider wearing ear protection.
Professor Deepak Prasher, head of University College London's Audiology unit, took the measurements on four Victoria Line journeys.
LU said it was aware of the problem but it was unlikely to affect passengers.
Prof Prasher found that the noise peaked at 118dB, louder than a pneumatic drill, and found the average level was between 88 and 89dB.
Health and Safety rules state employers should provide ear protection for people exposed to average levels of 85dB over an eight-hour period.
Prof Prasher: "I am shocked by the levels that we actually recorded. They were peaking at 118dB which is quite horrendous.
"The squealing and so on near Stockwell and Pimlico is quite astonishing really.
"It's the equivalent of a big jack hammer going, or a jet engine taking off in the distance.
"Although the journey times for most people are going to be short, this is a cumulative damage.
"If you regularly commute and use that line, then you need to seriously think about some form of ear protection."
He also tested a student's hearing before and after a Victoria Line journey and found sensitivity fell immediately after the journey - although it soon improved.
A Tube train driver, speaking on condition of anonymity, told BBC London that he always wears ear protection.
He added: "I would advise passengers to do the same, it really is very noisy indeed, and they shouldn't put their hearing at risk."
Dr Olivia Carlton, LU's head of occupational health, said: "Certainly the Underground is noisy and it is something that we are very aware of.
"We monitor our own staff's hearing on a regular basis, and we've looked at the hearing of train operators and we haven't actually ever demonstrated noise induced hearing loss.
"Although I would agree that the underground is noisy, and particularly in certain areas, it seems rather unlikely that our customers hearing would be damaged because their journey time is much shorter than our train operators."
She added: "On the Victoria Line we are aware that there is a problem and we have got a programme planned."
Prof Prasher has called for a funded programme of research into the impact of noise on LU.