unlikely for both speakers to develop the fault, as has been said its more likely to be a connection or something.
If it turns out that it is the speakers,then its not a big deal to replace, just get ones of same dimensions or as close as you can so they fit, same impedance and wattage (somewhere like maplins should have something).
If you have model number a search online may well give you the exact speaker specs, the manual may have the speakers output in watts but probably wont have the impedance which is usually in ohms.
the old ones may well have it on a label on the back of the speaker
speakers normally only have two connections a positive and a negative, red and white or maybe black and a white, its not a big job.
There is an alternative and that is if the TV has an audio out or headphone socket then you could get some external powered speakers and connect those up instead. Plenty of really good and relatively cheap PC speakers out there
might be worth checking with some headphones if the audio out socket signal is clear or has the same problems the speakers do.