From the Guidelines

The murmur associated with aortic stenosis (AS) is typically characterized as a loud, late-peaking systolic murmur that radiates to the carotids.

The murmur is usually grade 4/6 in severity
It is a systolic ejection murmur, meaning it occurs during the systolic phase of the heartbeat
The murmur radiates to the carotids, which can help distinguish it from other types of murmurs
In some cases, particularly in the elderly, the murmur may be soft or radiate to the apex instead of the carotids

A single or paradoxically split second heart sound (S2) is often associated with severe AS
A delayed and diminished carotid upstroke is also a common finding in severe AS, although this may be normal in the elderly due to the effects of aging on the vasculature
The only physical examination finding that is reliable in excluding the possibility of severe AS is a normally split second heart sound 1

Echocardiography is recommended for the diagnosis and assessment of AS severity, as well as for re-evaluation of patients with known AS and changing symptoms or signs 1
Transthoracic echocardiography is recommended for re-evaluation of asymptomatic patients with AS, with the frequency of re-evaluation depending on the severity of the disease 1

From the Research

The loudness of the murmur in aortic stenosis correlates best with peak momentum transfer, and thus with body size, so that loud murmurs predict severe disease less reliably in larger patients 2
The murmur of AS is typically identified by its characteristics, such as maximal murmur intensity at the second right intercostal space, and associated findings like slow carotid artery upstroke and reduced carotid artery volume 3
The presence of a murmur over the right clavicle is an important clue to the presence of aortic stenosis, while the absence of a murmur over the right clavicle rules out aortic stenosis 3
Auscultatory characteristics of the murmur, such as the timing and location of the murmur, can be used to evaluate the severity of aortic stenosis 4
Clinical context, including symptom status, prior knowledge of diagnosis, and patient factors, can affect the detection of the murmur of AS 5

Slow carotid artery upstroke and reduced carotid artery volume are associated findings that can indicate severe aortic stenosis 3
Reduced intensity of the second heart sound can also be an associated finding in patients with aortic stenosis 3
A weak or impalpable carotid pulse can indicate critical aortic stenosis, especially in the presence of an aortic stenosis murmur 6