air intake vibration

A mate of mine bought a diesel 94' hilux recently. On the weekend he went to replace the air intake pipe cos it had a crack that had been patched up by previous owner. when he took it off he found the patch job was to put a piece of pipe inside , but the pipe had the ends half closed off restricting the air flow to the engine. The ute is fitted with a after market snorkel and when the pipe was replaced, withpout the air flow restriction, when he reaches 2500 revs the air cleaner box vibrates rather loudly. By putting the snorkel on this would have increased intake volume so i gather the previous owner has put in this restiction to stop the engine drawing so much air and vibrating. Seems ludicrous to do try and stop vib's this way by restricting engine air flow. Tried a few things to stop it but nothing has worked so far. Any comments, experiences or advice how to stop this vibration without restricting the flow woul be appreciated. (Increase in power was quite noticeable when restiction was removed)