''thud'' sound when starting

Could be a motor /transaxle mount loose or worn out.

Water on the ignition coils

There are many possibilities that can cause car to make noise.

There is N-number of possibilities for the car to make thud noise or any other kind of noise.

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For step by step troubleshooting this problem, I suggest you to refer the help links mentioned below. Its a complete solution with proper explanation to identify the cause of problem: ------

Click the link below: -----

Vehicle making Clunk Thump Thud noise?

http://howtobyme.blogspot.in/2012/03/vehicle-making-clunk-thump-thud-noise.html

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Car makes clicking noise?

http://howtobyme.blogspot.com/2011/11/car-makes-clicking-noise.html

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Car makes whining noise like driving on rough pavement?

http://howtobyme.blogspot.com/2011/12/car-makes-whining-noise-like-driving-on.html

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Chirping Noise From Car?

http://technoanswers.blogspot.com/2011/11/chirping-noise-from-car.html

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What are the possibilities for Clicking noise in car?

http://technoanswers.blogspot.com/2011/11/what-are-possibilities-for-clicking.html

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Squealing at start up on car?

http://technoanswers.blogspot.com/2012/01/squealing-at-start-up-on-car.html

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Chirping sound coming from engine?

http://technoanswers.blogspot.in/2012/01/chirping-sound-coming-from-engine.html

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4X4 Truck makes roaring noise in the front end?

http://schematicsdiagram.blogspot.com/2012/01/4x4-truck-makes-roaring-noise-in-front.html

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Heater makes clicking noise under dash on Ford Explorer?

http://technoanswers.blogspot.in/2012/01/heater-makes-clicking-noise-under-dash.html

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Clicking noise under dash and front defroster not working?

http://technoanswers.blogspot.com/2012/01/clicking-noise-under-dash-and-front.html

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Car Brakes Making Noise?

http://repairhelpcenter.blogspot.com/2011/12/car-brakes-making-noise.html

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Car Alternator making noise?

http://repairhelpcenter.blogspot.com/2011/11/car-alternator-making-noise.html

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Car Alternator Bearing Makes Grinding noise?

http://repairhelpcenter.blogspot.com/2011/12/car-alternator-bearing-makes-grinding.html

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Engine makes noise and Cooling Fan belt Breaks?

http://howtobyme.blogspot.com/2011/12/engine-makes-noise-and-cooling-fan-belt.html

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Vehicle Makes Clicking Sound While Taking turns?

http://schematicsdiagram.blogspot.com/2011/12/vehicle-makes-clicking-sound-while.html

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ABS light comes on and Car makes Grinding noise?

http://repairhelpcenter.blogspot.com/2012/01/abs-light-comes-on-and-car-makes.html

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These will help.

Thanks.

motor mount is out or tranmission mount

here are few components that can cause such problem.Its advisable to click the link below and follow the troubleshooting to correct the problem.
Engine makes noise? http://howtobyme.blogspot.com/2011/12/engine-makes-noise-and-cooling-fan-belt.html

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Chirping sound coming from engine? http://technoanswers.blogspot.in/2012/01/chirping-sound-coming-from-engine.html
--------- Vehicle making Clunk Thump Thud noise? http://howtobyme.blogspot.in/2012/03/vehicle-making-clunk-thump-thud-noise.html

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Car Engine Overhaul Tips? http://vwrepairhelp.blogspot.com/2011/11/car-engine-overhaul-tips.html

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HOW TO PERFORM A BASIC ENGINE TUNE UP-OIL CHANGE
http://schematicsdiagram.blogspot.com/2011/08/how-to-perform-basic-engine-tune-up-oil.html

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Rattle noise from engine? http://whatisbyme.blogspot.in/2012/05/2005-toyota-corolla-rattle-noise-from.html

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These will help.
Thanks.

Could be internal damage. Put a socket and wrench on the crankshaft pulley and see if engine is seized up. The thud is worrying, suspect major damage if the crank won't turn all the way round. If you can't turn the engine by hand, you will need a new engine (or new vehicle- that is a pretty old suburban, almost ancient to be needing a new engine!)
If engine still turns by hand, have your starter tested.

Cant rule that out. If car has ever been in an accident you want want to check the engine mounts also. This sometimes sounds just like a transmission going out of a vehicle.

Possibly 2 conditions at once. If it is sitting at an idle and you hear the thud noise, it very well depends on where you are hearing it but it almost sounds to me like maybe occasionally the is backfiring.I would personally if this is the case, Take air filter housing away from the motor and check the throttle body for a buildup,check air filter, and try some fuel treatment.If you have no check engine light it is not mis firing, but it could be exhaust related.

sorry to tell you this but the final gunning of the engine your mate did sounds like the cambelt has gone ! to check try turning engine using spanner/socket on the crank pully if it turns backwards but not forward ? this indicates the pistons are hitting valves this can/will be expensive damage considering what happened prior to sudden failure and it is more than likely that the belt squeal you heard was in all probability the cambeltand tensioner failing ? you will need to remove cyl/head to investigate damage ? consider milage of engine? b4 you decide repairing and it may well be a better option to fit a recon or 2nd hand lower milage from breakers ? hope this helps? please come back with update or if you req info/help

Clicking noises on turns may indicate that you have a broken constant velocity joint boot on the front axle. Check that and see if it is torn. It''s the black bellows-looking thing right behind the inner spindle. If it is torn, all of the grease has leaked out, and the clicking is the joint rattling.