How to eliminate the hum and hiss in the speakers?

Question

Electronics

Problem: The Sven SPS-611S 18W speakers started making extra noise in the form of hiss and hum. When buying, I checked for extra noise for a long time, everything was clean. It all started after 1.5-2 years of use. It's quiet at first and you can't hear it until you get close. Now (about 3 years of use) it is clearly audible at a distance of 3-4 meters in a quiet room, it is also audible when watching quiet scenes in films.
What he did: changed wires, connected to a laptop, phone, tablet, to another outlet. There is nothing strange inside: nothing has melted, there is no burning smell, the conders have not leaked, etc. The voltage in the outlet is normal. It does not heat up inside, at maximum power it heats up within the permissible limits, it does not burn. They stand next to the LCD TV, changed the location, there are no sources of interference nearby. Other speakers cheap Sven and Microlab with the same computer work without unnecessary noise.
What to check, where to dig further?

Answer 1

Google the diagram .
Critical capacitors - C15, C16, C17, C18.
We buy and sell.
And maybe better .
By the way, here are the instructions .

Answer 2

Capacitors could not leak, but simply lose capacity, dry out. Most likely this is the case. There is nothing more to rot there.

Answer 3

I would look with an oscilloscope at the output from those capacitors, for sure there are ripples. You can change them right away, it will not be worse.