I replaced my old chain with a new one. After changing the chain I notice that standing pedaling uphill and flat surface in 4th or 5th gear the cogs will engage/disengage. But when I put the old chain back on, the problem is gone. The cogs/cassette is 2 years old and I use it on both trail riding and XC.
Is the new chain the problem or do I need to replace the cassette/cogs when I install a new chain?