help please knocking on 300tdi engine

just ordered a set of these off ebay

LAND ROVER 300 TDI NEW INJECTOR NOZZLES SET OF 4 on eBay (end time 30-Oct-10 20:21:15 BST)

what condition is the alternator belt tensioner in?
does it bounce up and down? (when engine running)

had these produce a knockin noise before.
check carefully by putting pressure on arm behind pulley, using blunt object (hammer shaft). has to be done with engine running so be careful.
it doesent cost owt to do, an eliminates the tensioner.