Really loud rattling coming from the front of my truck

[WRXtranceformed]

This sound just started up today. My mechanic said over the winter my truck lost a bit of coolant, so he thinks the head gasket may be going. He could find no leaks though. Any ideas off hand what the fuck this sound is? It sounds like a gigantic tin can with boulders in it is rattling around in my engine bay.

I don't seem to be losing coolant right now, but my truck definitely feels noticeably weaker...

[white_2kgt]

when do you/don't you hear the noise? at idle, at wot, at 40-55mph, only when you have the radio on some really stupid channel and your head cocked about 10* to the left? does it increase with RPM? does it increase with speed?

[WRXtranceformed]

I hear it at a little over half throttle. If I get up to speed and cruise, it goes away, but the second I put my foot more on the gas it comes back. It also completely stops when I press in the clutch. It seems to happen in every gear now except for 1st. It definitely gets louder with speed and RPM.

[Evan]

tin can w/ boulders when on the gas sounds like detonation to me

try putting in some premium on your next fillup and see if it changes

[Maengelito]

heat shield perhaps? if its a truck, chances are its been worked a bit and may have rusted heat shields. a leaky headgasket wouldnt rattle, but that could be a completely different headache

[WRXtranceformed]

Hrm, both of them sound very feasible. I threw an 02 sensor CEL about a month ago, but it went away on its own. I wonder if the two are related.

My truck is pretty old though and it wouldn't surprise me if something finally worked its way loose under the hood. I'll have to have my brother check while I rev it.

[Evan]

if it makes the noise while at idle, then its not detonation. Detonation happens when the car is under load. The more load, the more detonation.

I screwed up Miata engine #1 (worse than it already was screwed up) by accidentally setting the timing to 22 degrees BTDC. It sounded like a tin can drumroll everytime I stepped on the accelerator and the power was way down. Of course i drove it like that for 3 weekends on track.......

[WRXtranceformed]

What could suddenly cause detonation in this engine? It's not like mine where I turn up a knob and it goes boom, it's not turbo'd or anything.

[HAULN-SS]

Maybe that O2 sensor is malfunctioning causing it to send a rich signal to the computer - thus leaning out the mixture

[Maengelito]

rattling can happen at certain rpm's as well, i guess certain frequencies from different engine rpms would work the heat shield causing it to rattle. i think the cat's heat shield on my sti rattles ever so slightly at around 3400 rpm. its sometimes audible under acceleration but its usually when i'm slowing down. when the needle dips down to about 3400, it rattles for a split second then you cant hear it after that

[WRXtranceformed]

I might try resetting the ECU tomorrow, and see if I can hear anything at idle when I rev it up. Come to think of it, I used to notice this sound a lot if I was slowing down to like 10mph and I was still in 3rd gear. This would cause the engine to shake a lot and i would hear the noise. Maybe whatever it was has worked its way loose finally.

Or maybe another one of my blocks is about to asplode... who knows ! =p

[Jeff]

Think about the waterpump bearings? Maybe they took a shit. Grab the WP pully and shake it like you would a tire and see if it is loose.