Can abdominal aortic aneurysm diagnosed with a sthethoscope exam or you need an ultrasound scan?

Diagnose AAA. While some large aneurysms can be felt with your hands on the belly an ultrasound is a much more effective and accurate way to make the diagnosis.
Ultrasound is best. Physical exam is unreliable; doctors over diagnose abdominal aneurysms in thin people and underdiagnose them in fatter people on physical exam alone. The best screening test is a duplex ultrasound. In experienced hands, this test has a 99% plus sensitivity and specificity-- meaning it is a very good screening test.
Imaging is better. Ultrasound, ct, and MRI are superior to physical exam.