shuddering engine noise--- 01 i30

[rubs]

The engine in my '01 infiniti i30 (55,000 miles) has been making a noise that was subtle for a while and now has become quite loud. It sounds like someone banging on the engine block with a hammer. It's most prevalent at idle or speeds under 30mph after driving normally for 30-40 min. It almost feels like engine will explode ..shaking is in pedal as well as stering. What can be the possible issue:Coolant flush/Water pump Transmission fluid (replace at 30k and should go until 90k)Spark plugsAny advice will be appreciated.

Thanks--rubs

[audtatious]

Do you have any codes?