The speaker has probably had it. My garmin i3 suffered this fault. Connecting aother 1w speaker works fine - IF you can find one!?!?!?!? Don't know about the C510 but the speaker in the i3 is an 8ohm, 1watt 50 mm dimatere speaker - part number 36CS08FN-3-1. I think the c510 is same or similar.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix satellite navigation.