also, buses and trucks make all sorts of noises so it's a little vague... but yeah more info would be a great help.
but if by grinding, you mean like a high pitched squealing (think train screeching to a stop), then perhaps you need to look at if any area around your clutch/flywheel are worn, or for mechanical failure. if this sound only occurs when engaging (partial clutch), i would suspect any or a combination of the issues Koala listed above.
also, the clutch should be used in as short a time as necessary when engaging a gear.
'13 CRZ - PWP EX 6MT