Clunking sound at high speeds

ljonski

I have booked it in at a cycle shop tomorrow for a service,but thought i might get some idea on here about what the problem is. Its a Giant TCR road bike with less than 400 miles on the clock. I bought it new in september. This is the 3rd time it has happened and it only happens at approx 30 miles p hour and above. In fact there are two noises behind me a screeching sound and on sunday a very loud clunking sound. As the noise is behind me and i am going pretty fast down hill it is impossible to see where exactly it is coming from and I am braced for the back wheel to jam and cause a bad fall. I am not doing any hill rides until i find the answer and it is rectified. It is a quick release wheel and appears to be on properly TIA

rdr

Untoed in brake blocks and a rough join in the rim?

maninthestreet

It will be the pedestrian you knocked down....

ljonski

its gone in now for a service and speaking to the guy at the desk , he couldn't immediately see what is wrong. I am not sure aboutthe brake blocks as i think it happens at least teh screeching before brakes are applied. - but thanks for your input.

markelock

is it your knees?

mine creak? I'd like to think it's power, but it's probably weight...

ljonski

well the mechanic couldn't [put his finger on the problems, except tightening the headset. I am off for a hill climb on sunday but first i ,m off to check my will is in order..............

DevCoder

Possible rear bearing issue? If something is out of alignment then the more force (speed, centrifugal) you put on it the worse it will be.

rugbyleague

Check wheel bearings (borrow another wheel?)
Its not your chain rubbing on the front mech is it?
Have all moving parts got a small amount of oil on?
Wheel rubbing on mudgard, cycle computer magnet catching?

clutching at straws a bit, spokes tight?

Does it do when you are pedalling or free wheeling (trying to eliminate drive train)?

Just some thoughts its rubbish when theres something not quite right isnt it?

ljonski

Well Im still here after much too-ing and fro-ing to the bikeshop and back and 2 more hill climbs and descents, to try to get to the bottom of the problem.
its not my knees nor is it the pedestrian that i hit.
Initially the bike shop couldn't find the problem let alone solve it. They took it for a test ride and did some maintenance, but where at a loss to know what it was.
I told them that i would take it for a sharp descent and see if i could have a shifty at it whilst doing 30 mph down a twisty hill! The clunking was the chain hitting the frame! i tried it on the big cog today and it was much better although the back wheel sounded as if The Flying Scotsman was in hot pursuit.
At the bottom of the hill I was able to replicate the screeching by pedalling backwards and freewheeling.. I did this also in the bike shop and the guy said he'd never seen anything like it before. He's going to clean the freehub and have a look to see if anything is broken. First time he told me to contact CRC as it is under warranty, although I will e -mail CRC as he said they should pay for the repair.

The derailleur is pushed forward whilst this happens and hence the chain becomes slack.

Has anyone had any problems getting internet bike shops to cough up for repairs whilst under Warranty?