strange audio humming noise

quartzz

Hello

I have a strange buzzing noise that sometimes comes from a laptop/subwoofer setup under certain conditions. laptop is a fujitsu lifebook a531, sub is this

https://www.amazon.co.uk/Trust-21787-Surround-Speaker-System/dp/B07643GD6Q/ref=sr_1_2

it happens under the following conditions

hum is virtually silent at subwoofer bass dial set to minimum. hum gets louder as subwoofer bass dial is turned up to halfway, hum dies down to almost nothing as sub bass dial goes to maximum

hum is made worse when an hdmi cable (2 metres long) connected to a TV is plugged into the laptops hdmi port

my gut instinct is that its to do with the laptops internal earthing. educated guess. I've just ordered a new hdmi cable, which should get here in a couple of days. but the hdmi cable I'm using at the moment isn't a cheapy

any ideas welcome..? more info can be given

The sub is still under 30 day trial so I can send it back for a replacement

thanks

next010

Not sure really, do you have an external USB sound card, maybe that could separate itself from whatever is going on internally though USB audio is known to sometimes be prone to interference too.

Their are dirt cheap USB sound cards on Amazon and some more costly ones from Creative Labs.

Backspace

Sound like a broken ground loop. Try wiring a wire chassis to chassis (ground to ground).

12harry

What is odd is the effect you say of the Sub-level control. But you omitted to say if the Sub (on its own) is OK.  These effects are often difficult to discover - except by trying/replacing everything in turn.
In the past, amps had an earth terminal - but this was in the days when hum was an issue due to relatively poor PSU components - nowadays with switch-mode the psu-hum issue is all but over, since ripple at the switching frequency is so much easier to filter. Of course it could be the s-m  PSU's are at different frequencies ( very likely) and the hum is a beat-freq.... however, I'd expect the designers to have thought of this.
So, unless this is a "Well known fault" the chances are you've truly got a odd one . . . .

If you can be bothered, ( and you should, as it will only appear to get worse! ), send it back and hope the replacements are much better.
Good luck.