I had very similar symptoms - but on a very cheap bike. I ignored the clicking - which I initially thought was perhaps a loose spoke on the front wheel - until yesterday, when the whole wretched bike came to a halt on my way to an important appointment.
Turned out to the be bearings on the
rear wheel, had to buy a new wheel. Fortunately, bloke at LBS took one my bike, declared it a P.O.S. (I already knew that!), and suggested cheapest poss option was a reconditioned wheel at £23. Much cheaper than I had feared! Props to the guys at
Picton Cycles who dealt with me just as attentively as the guy at the counter blowing £1,500 in readies on a
fancy new MB.
Missed the freakin' appointment of course. Oh well, teach me to ignore ominous creakings & clickings!